The Structure of Humic Substances in the Agricultural Genetically Modified Soils of the Kansk Forest-Steppe

In two long-arable areas that were intended for sowing rapeseed and false flax for oilseeds at LLC «Experimental Industrial Farm Solyanskoye» in the Kansk forest-steppe, the structure and humus substances reserves in agrochernozems were studied. The soil cover of key plot No. 1 with the wide-steeply-sloping terrain with weakly pronounced microrelief, which was intended for rape, was dominated by typical medium and strong clayey-illuvial agrochernozems. Key plot No. 2 intended for false flax was located on a smooth hillside of a wide ridge and was characterized by the complexity of the soil cover represented by a combination of clay-illuvial typical agrochernozems of various kinds, thick podzolized clay-illuvial agrochernozems, and thin cryogenic micellar agrochernozems. It has been shown that agrochernozems featured high content of humus in the layer both 0 – 20 and 0 – 40 cm thick. The content of humus carbon (Ctot) and that of carbon of the water-soluble organic matter (CH2O) had little spatial variability (CV = 1.3 – 11.7 %), unlike the carbon content of the alkali-soluble organic matter (C 0.1 n. NaOH), which in the studied agrochernozems had a very high degree of spatial variability (Cv = 18.7 – 66.1 %). Heterogeneity of the soil cover of the slope part of the plot was the factor that determined the average reduction in the content of the reserves of all fractions of humic substances, except for the water-soluble humus carbon. It has been found that the share of the reserves of stable humus carbon (Cstab) was 89 – 95 % of the total carbon reserves of humus, thus the share of CH2O and C0.1 n. NaOH decreased with increasing the complexity of the soil cover from 11 to 5 % of Ctotal. Fields with a pronounced meso- and microrelief and thin kinds of agrochernozems are recommended for sowing false flax, which is a crop that is less demanding to the soil conditions than rapeseed.